The general specifications for the number of electrical conductors between heavy duty truck tractors and trailers operated in the United States and Canada long have been governed by Society of Automotive Engineers (SAE) Standard J560 (“SAE J560”), the current version of which is incorporated herein by reference. SAE J560 also governs the arrangement and sizing of terminals of connectors (plugs and sockets) for tractor-trailer electrical connections, and also the basic geometries of those connectors. The objective of SAE J560 is to assure the electrical interconnectibility, without the use of adapters, of any truck trailer to any truck tractor. Other SAE standards address that interconnectibility objective in the context of mechanical and pneumatic connections between truck tractors and trailers. In other parts of the world, standards having the same objective, but different specifics, are applicable.
The SAE J560 connectors used to make electrical connections between truck tractors and trailers are sockets and plugs. The sockets most commonly are mounted to the opposing faces of tractors and trailers. The plugs are carried at the opposite ends of tractor-trailer interconnection cables. Sockets typically are mounted in holes formed in the rear walls of tractor cabs and in the front end walls of trailers, so that a portion of the socket is outside the vehicle and a portion of the socket is inside the vehicle. Generally, the front of the socket is outside the vehicle and the rear or back of the socket is inside the vehicle.
In tractors currently produced, the electrical connections to a mounted SAE J560 socket are complex and involved. Those connections typically are made by use of one or more multi conductor harnesses, one end of which can be a socket that mates with the terminals extending from the rear of the mounted J560 socket. The harness conductors extend from that harness end socket to various places in the tractor, such as to the battery, and to function switches and controllers, which in turn are connected to the battery. Some of these harness conductors are part of extensive circuits which include long conductors and many connectors. The result is that the power applied to the SAE J560 socket terminals frequently has a voltage less than the desired full battery voltage. The problem of low SAE J560 tractor socket terminal voltage is a problem shared by tractor manufacturers.